Color filters are generally produced by a method in which, on the surface of a transparent substrate in which a black matrix is formed such as glass or a plastic sheet, different hues of red, green, and blue are sequentially formed in a color pattern such as stripes or mosaic. The black matrix used as a light-shielding film serves to prevent the decrease in contrast and color purity due to light leakage between pixels.
Also in a substrate for a touch panel, a black matrix is formed likewise as a light-shielding film, and since the black matrix is directly viewed through glass, the reflected hue is required to be achromatic. Further, depending on the constitution, it is necessary to form electrodes and the like after forming a black matrix, and, accordingly, high adhesion and chemical resistance as well as high insulation properties are required.
Conventionally, films on which a metal such as chromium, nickel, or aluminum or a metal compound is deposited have been used as a black matrix, but they have problems in that, for example, the process is complicated and costly, and the surface of the metallized thin film is highly reflective. Thus, as a method that can solve these problems, the pigment dispersion method which uses a resin composition in which pigments are dispersed is currently predominant.
In the pigment dispersion method, among negative and positive photosensitive compositions, negative photosensitive compositions mainly composed of acryl polymer, acrylic polyfunctional monomer or oligomer, photoinitiators, solvents, and pigments have been widely used. As a light-shielding material, carbon black, titanium black such as low-valent titanium oxide and titanium nitride oxide, metal oxides such as iron oxide, and, in addition, mixtures of organic pigments have been used, and carbon black and titanium nitride oxide are predominant. To obtain a black matrix having high insulation properties, surface-treated carbon black and titanium black, or those mixed with organic pigments have been used as a light-shielding material.
As a technique for providing a carbon black with high insulation properties by surface treatment, oxidizing the surface of the carbon black, for example, with O3 (Patent Document 1), resin coating by graft treatment (Patent Document 2), and modifying the surface of the carbon black with an organic group that does not comprise a polymer, such as a carboxylic acid group and a sulfonic acid group, (Patent Document 3, Patent Document 4, and Patent Document 5) are known, but there has been a problem in that when a resin black matrix is heat-treated at a high temperature, e.g., 250° C., the resistance decreases.
When titanium nitride oxide or a titanium nitride compound is used as a light-shielding material in a photosensitive resin material, a resin black matrix having a sufficiently high resistance value can be readily formed, and the resistance value will not decrease even when the resin black matrix is heat-treated at a high temperature. However, the resin black matrix obtained using titanium nitride oxide or a titanium nitride compound has a problem in that the transmitted light is colored blue and the reflected light is colored red. Patent Document 6 describes adding carbon black to titanium nitride oxide, but there have been problems in that when toning is performed by adding carbon black to titanium nitride oxide, the OD value decreases, and, in addition, a sufficient resistance value cannot be obtained. A resin black matrix having high resistance and relatively achromatic color properties can be obtained by using a titanium nitride compound with a small particle size as a light-shielding material (Patent Document 7), but for touch panel application and the like which strictly require reflected light chromaticity, a more achromatic color has been necessary.
Further, when a material mixed with organic pigments is used as a light-shielding material (Patent Document 8), a black matrix having high insulation properties can be obtained, but there has been a problem in that because of a low light-shielding effect per unit film thickness, the film thickness needs to be thick in order to produce a desired light-shielding effect, which deteriorates the flatness of the boundary with openings of the black matrix.